In recent years, attention has been given to hybrid vehicles as environmentally friendly vehicles. The hybrid vehicle is equipped with an electric motor as a drive power source for vehicle running in addition to a conventional internal combustion engine. Japanese Patent Laying-Open No. 2006-62569 has disclosed a technique that allows a driver to select a manual shift mode for gear shifting in this hybrid vehicle.
A shift device disclosed in Japanese Patent Laying-Open No, 2006-62569 controls the hybrid vehicle in which an engine, a first electric motor and a second electric motor connected to drive wheels are connected together via a planetary gear mechanism. This shift device includes a shift level to be operated for selecting a plurality of shift positions. This shift lever can be selectively shifted by a manual operation to a parking position, neutral position, forward automatic shift position (D position) and forward manual shift drive position (M position). In the M position, an up-shift position “+” and a down-shift-position “−” are aligned to each other in a longitudinal direction of the vehicle. When a driver shifts the shift lever to the up-shift position “+” or the downshift position “−”, a “D” range or an “L” range is selected. Thereby, the shift control is performed so that a gear ratio may not exceed a ratio on a maximum speed side of the shift range.
In the hybrid vehicle disclosed in Japanese Patent Laying-Open No. 2006-62569, as described above, the revolution speeds of the engine and the first electric motor are controlled not to exceed the gear ratio on the maximum speed side during the running in the manual shift mode. However, even during the running in the manual shift mode, the engine may not attain the revolution speed corresponding to the gear ratio on the maximum speed side, but may be controlled to attain an idle revolution speed when the vehicle is in a self-sustained drive state, i.e., when the first electric motor is controlled to output a torque of substantially zero and the engine is controlled to stay in an idling state. Therefore, when a large difference is present between the revolution speed corresponding to the gear ratio on the maximum speed side and the idle revolution speed, the engine revolution speed changes rapidly to cause a shock in the vehicle whenever the state is switched between the non-self-sustained drive state and the self-sustained drive state.